40 CELLTJLAHIID^. 



have received abundant specimens, through Dr. Dawson, 

 from the Gulf of St, Lawrence, is properly accounted a 

 variety. It differs very slightly from M. arctica, Busk*. 

 The lateral avicularium is not developed on the upper- 

 most cell, but is usually present on both the others, 

 occasionally only on one of them. It varies much in size: 

 sometimes on the same internode one of the avicularia is 

 very much larger than the other, attaining comparatively 

 gigantic dimensions. On the whole the size of the lateral 

 appendages is remarkable in this species. The anterior 

 avicularium I have generally found on the front of the 

 terminal cell above, and nowhere else. But it is some- 

 times developed on every cell, and is so figured by Busk. 

 It is very minute, as we should expect, considering the 

 large size of the lateral appendages. The changes in the 

 form of the operculum are simply due to differences in 

 the stage of development. Regarded morphologically, it 

 is a modified spine ; and in its first stage it appears as a 

 simple spinous process. It gradually expands into a 

 broad protective shield or lamina ; as it enlarges ex- 

 tension takes place chiefly in the direction of the bottom 

 of the cell. When mature it is suboval or somewhat 

 wedge-shaped. The spines vary in number. There are 

 sometimes three or four, frequently only two. One of 

 them is usually placed some way doAvn on the outer 

 margin, almost fronting the operculum ; and it is often 

 enormously develoi)ed, exceeding the internode in height. 

 * Habitat. On Algee in the littoral zone, and on various 

 Hydroida (chiefly), shells, &c. from shallow to deep water 

 (100 fathoms). 



* I have received from Mr. Peacb two or three minute fragments of a 

 Menipea from Shetland, in which the form of the cells is that of the gracilis 

 variety. They also show a larger number in the internode than is chai-ac- 

 teristic of the normal M. tcrnata. But their condition is too imperfect to 

 allow me to determine whether they should be referred to this variety, or to 

 one of the closely related forms M. arctica and M. Smittii. 



